Update git submodules

Update git submodules

* Update docs/submodules/functest from branch 'master'
  - Merge "Revert rally version to 0.8.1"
  - Revert rally version to 0.8.1

    1. Now rally version 0.9.1 is installed via "bash install_rally.sh
       --yes", cause the default RALLY_GIT_BRANCH is master. Then
       some rally related tests will fail as rally tests have not been
       updated in functest
    2. rally version 0.8.1 can be installed via --branch 0.8.1

    Change-Id: I04003134f070a1a35db2c02f2209e77365be592f
    Signed-off-by: Linda Wang <wangwulin@huawei.com>